/* requestAnimationFrame */
window.requestAnimationFrame = 
      window.requestAnimationFrame || window.mozRequestAnimationFrame || 
      window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
 
/* cancelAnimationFrame */
window.cancelAnimationFrame = 
      window.cancelAnimationFrame || window.mozCancelAnimationFrame || window.msCancelAnimationFrame;
